Shrinkwraps Not Following Head - Pupil Shrinkwrap Not Staying On Eyes When Rotated
Here is the Link to explain what I would change 



These are the primary things I felt I would change if this were my own.



I would use an Empty for the focal point (instead of a bone) and parent it to the armature.

I would get rid of the two empties at each pupil.

I would tell each pupil to track (constraint) to the "NEW" focal point empty.

I would tell each pupil to pivot (constraint) to the "Head" bone.

Here is the result of doing these four things.